Thomas Barnes, 48, was filling his tank at the BP station on East 119th Street and First Avenue at around 11 a.m. when he saw gunman Rudolph Wyatt running from the store, and sprang into action.

He crouched behind his hedge-fund boss’ Mercedes SUV and squeezed off three shots, killing Wyatt, 23.

The trigger-happy thug — wanted on warrants for two other shootings — lay dead in a pool of blood on the sidewalk wearing a black stocking mask with a wad of stolen cash spilling out of his pocket, witnesses said.